ASTRONOMICAL HISTORY. 1G3 



Nicetas of Syracuse, and particularly of Philolaus, also in 

 our age of Gilbertus, and all, (except Galileo), who have held 

 that the earth is a planet, moves, and is, as it were, one of the 

 stars. And this idea has solidity thus far, that the planets 

 and single stars, and the countless number which from their 

 distance baffle our vision, and others also unseen by us, from 

 their being not of a luminous but opaque nature, each in its 

 respective orbit and primary tour through that illimitable 

 expanse which we behold, whether of vacant space or of 

 some subtler and almost indiscernible substance, are dis 

 persed and lie about like islands in a vast ocean, and 

 revolve not upon a common centre, but each upon that of 

 its respective orbit, some absolutely, others with some 

 progressive motion of their own centre. There is one 

 very great difficulty in their opinion, namely, that they 

 altogether banish rest, or an immoveable point from na 

 ture. Now it seems that, as there are in nature re 

 volving bodies which are borne along in interminable and 

 ceaseless motion, so, on the contrary, there ought to be 

 some body which is quiescent; between which we place 

 the intermediate nature of those which are carried in a 

 straight-lined path, since motion in a straight line is suit 

 able to fragments of spheres, and things exiled, so to speak, 

 from their natural seats, which move towards orbs homo 

 geneous with themselves, in order that, united with these, 

 they may either be rotatory or quiescent. But of this ques 

 tion, whether there be a system, a conclusion will be obtained 

 by means of those which relate to and determine the motion 

 of the earth, whether the earth revolve or be at rest, and 

 to the matter of the stars, whether it be solid or igneous ? 

 For if the earth stands still, and the heavens perform a 

 diurnal revolution, undoubtedly it is a system ; but if the 

 earth be rotatory, it is nevertheless not absolutely proved 

 that it is not a system, because we may still fix another 

 centre of the system, such as the sun, or something else. 

 Again, if the orb of the earth alone is crass and solid, it 

 seems as if the matter of the universe was agglomerated and 

 condensed into that centre : but if the moon and other planets 

 are found to be also composed of crass and solid matter, 

 it seems that dense bodies do not unite in any centre, but 

 lie dispersedly, and so to speak, at random. Finally, if in 

 the interstellar spaces we place a vacuum coacervatum, then 

 the several orbs should seem to have round them, first, 

 the envelope of certain subtle effluvia, and then the va 

 cuum. But if these spaces are a plenum, there should 



